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United States Patent |
5,096,933
|
Volkert
|
March 17, 1992
|
Process for the preparation of polyurethane rigid foams having a low
thermal conductivity and their use
Abstract
The present invention relates to a process for the preparation of
polyurethane rigid foams having a low thermal conductivity, comprising
reacting:
a) organic and/or modified organic polyisocyanates with,
b) at least one higher molecular weight compound having at least two
reactive hydrogen atoms, and optionally
c) lower molecular weight chain extending agents and/or crosslinking agents
in the presence of,
d) cyclopentane (d1) or mixtures (d2) comprising, d2i) cyclopentane, and/or
cyclohexane, d2ii) at least one compound homogeneously miscible with
cyclopentane and/or cyclohexane, said compound preferably has a boiling
point below 35.degree. C. and is selected from the group consisting of
alkanes, cycloalkanes having a maximum of 4 carbon atoms, dialkylethers,
cycloalkylene ethers and fluoroalkanes, optionally combined with water as
said blowing agent (d),
e) catalysts, and optionally
f) auxiliaries and/or additives.
Polyurethane rigid foams are used in the low temperature appliance industry
and as insulating materials in heating and composite elements.
Inventors:
|
Volkert; Otto (IM Eiertal 10, 6719 Weisenheim, DE)
|
Appl. No.:
|
577174 |
Filed:
|
September 4, 1990 |
Foreign Application Priority Data
Current U.S. Class: |
521/131; 521/98; 521/99; 521/114; 521/115; 521/137; 521/160; 521/172 |
Intern'l Class: |
C08K 005/00; C11D 007/30; C08G 018/14 |
Field of Search: |
521/131,115,116,133,98,172,99,160,114,137
428/318.4
|
References Cited
U.S. Patent Documents
3586651 | Jun., 1971 | Salyer et al. | 521/113.
|
4555442 | Nov., 1985 | Frentzel | 521/116.
|
4572919 | Feb., 1986 | Londrigan | 521/137.
|
4996242 | Feb., 1991 | Lin | 521/131.
|
4997589 | Mar., 1991 | Lund et al. | 521/131.
|
Foreign Patent Documents |
2544560 | Apr., 1977 | EP.
| |
0389011 | Sep., 1990 | EP.
| |
0405439 | Jan., 1991 | EP.
| |
Primary Examiner: Kight, III; John
Assistant Examiner: Truong; Duc
Claims
We claim:
1. A process for the preparation of polyurethane rigid foams having a low
thermal conductivity, comprising reacting:
a) organic and/or modified organic polyisocyanates with:
b) at least one higher molecular weight compound having at least two
reactive hydrogen atoms, and optionally;
c) lower molecular weight, chain extending agents, and/or crosslinking
agents;
in the presence of:
d) blowing agents;
e) catalysts and optionally;
f) auxiliaries and/or additives;
wherein;
d1) cyclopentane; or,
d2) mixtures comprising:
d2i) cyclopentane, cyclohexane, or a mixture of these cycloalkanes; and,
d2ii) low boiling point compounds, homogeneously miscible with cyclopentane
and/or cyclohexane
are used in conjunction with water as said blowing agent (d).
2. The process of claim 1 wherein said mixture d2) comprises:
d2i) cyclopentane, cyclohexane, or a mixture of cycloalkanes; and,
d2ii) compounds having a boiling point less than 35.degree. C.,
homogeneously miscible with cyclopentane and/or cyclohexane, selected from
the group consisting of; alkanes, cycloalkanes having a maximum of 4
carbon atoms, dialkyl ethers, cycloalkylene ethers, fluoroalkanes, and
mixtures of at least two of the aforesaid compounds.
3. The process of claim 2 wherein said cyclopentane (d1) or said blowing
agent mixture (d2) is used in conjunction with water.
4. The process of claim 1 wherein said blowing (d2) has a boiling point
less than 30.degree. C.
5. The process of claim 2 wherein said blowing agent mixture (d2) has a
boiling point less than 30.degree. C.
6. The process of claim 1 wherein:
d1) cyclopentane; or,
d2) a mixture comprising:
d2i) cyclopentane, cyclohexane, or a mixture of these cycloalkanes;
d2ii)at least one compound selected from the group consisting of n-butane,
isobutane, cyclobutane, dimethyl ether, diethyl ether, furan,
trifluoromethane, difluoromethane, difluoroethane, tetrafluoroethane, and
heptafluoropropane;
are used as said blowing agent (d) in conjunction with water.
7. The process of claim 1 wherein;
d1) 3 to 22 parts by weight of cyclopentane combined with from 0 to 7 parts
by weight of water,
is used as said blowing agent (d) per 100 parts by weight of starting
component (b).
8. The process of claim 1 wherein;
d2i) 2 to 22 parts by weight of cyclopentane and/or cyclohexane;
d2ii) 0.1 to 18 parts by weight of at least one compound having a boiling
point less than 35.degree. C. homogeneously miscible with cyclopentane
and/or cyclohexane, selected from the group consisting of alkanes,
cycloalkanes having a maximum of 4 carbon atoms, dialkyl ethers
cycloalkylene ethers, and fluoroalkanes combined with from 0 to 7 parts by
weight of water;
are used as said blowing agent (d) per 100 parts by weight of starting
component.
9. The process of claim 1 wherein a mixture of diphenylmethane
diisocyanates and polyphenyl polymethylene polyisocyanate having a
diphenylmethane diisocyanate isomeric content of from 30 to 80 weight
percent are used said organic polyisocyanate (a).
10. The process of claim 2 wherein a mixture of diphenylmethane
diisocyanates and polyphenyl polymethylene polyisocyanate having a
diphenylmethane diisocyanate isomeric content of from 30 to 80 weight
percent are used said organic polyisocyanate (a).
11. The process of claim 1 wherein a mixture of diphenylmethane
diisocyanates and polyphenyl polymethylene polyisocyanate having a
diphenylmethane diisocyanate isomeric content of from 30 to 80 weight
percent are used said organic polyisocyanate (a).
12. The process of claim 3 wherein a mixture of diphenylmethane
diisocyanates and polyphenyl polymethylene polyisocyanate having a
diphenylmethane diisocyanate isomeric content of from 30 to 80 weight
percent are used said organic polyisocyanate (a).
13. The process of claim 4 wherein a mixture of diphenylmethane
diisocyanates and polyphenyl polymethylene polyisocyanate having a
diphenylmethane diisocyanate isomeric content of from 30 to 80 weight
percent are used said organic polyisocyanate (a).
14. The process of claim 5 wherein a mixture of diphenylmethane
diisocyanates and polyphenyl polymethylene polyisocyanate having a
diphenylmethane diisocyanate isomeric content of from 30 to 80 weight
percent are used said organic polyisocyanate (a).
15. The process of claim 6 wherein a mixture of diphenylmethane
diisocyanates and polyphenyl polymethylene polyisocyanate having a
diphenylmethane diisocyanate isomeric content of from 30 to 80 weight
percent are used said organic polyisocyanate (a).
16. The process of claim 1 wherein at least one polyhydroxyl compound
having a functionality of from 2 to 8 and a hydroxyl number of from 150 to
850 is used as said higher molecular weight compounds (b).
17. The process of claim 2 wherein at least one polyhydroxyl compound
having a functionality of from 2 to 8 and a hydroxyl number of from 150 to
850 is used as said higher molecular weight compounds (b).
18. The process of claim 1 wherein at least one polyhydroxyl compound
having a functionality of from 2 to 8 and a hydroxyl number of from 150 to
850 is used as said higher molecular weight compounds (b).
19. The process of claim 3 wherein at least one polyhydroxyl compound
having a functionality of from 2 to 8 and a hydroxyl number of from 150 to
850 is used as said higher molecular weight compounds (b).
20. The process of claim 4 wherein at least one polyhydroxyl compound
having a functionality of from 2 to 8 and a hydroxyl number of from 150 to
850 is used as said higher molecular weight compounds (b).
21. The process of claim 5 wherein at least one polyhydroxyl compound
having a functionality of from 2 to 8 and a hydroxyl number of from 150 to
850 is used as said higher molecular weight compounds (b).
22. The process of claim 6 wherein at least one polyhydroxyl compound
having a functionality of from 2 to 8 and a hydroxyl number of from 150 to
850 is used as said higher molecular weight compounds (b).
23. The process of claim 7 wherein at least one polyhydroxyl compound
having a functionality of from 2 to 8 and a hydroxyl number of from 150 to
850 is used as said higher molecular weight compounds (b).
24. The polyurethane rigid foams prepared according to the process of claim
1.
25. The polyurethane rigid foams prepared according to the process of claim
2.
26. The polyurethane rigid foams prepared according to the process of claim
3.
27. The polyurethane rigid foams prepared according to the process of claim
4.
28. The polyurethane rigid foams prepared according to the process of claim
5.
29. The polyurethane rigid foams prepared according to the process of claim
6.
30. The polyurethane rigid foams prepared according to the process of claim
7.
31. The polyurethane rigid foams prepared according to the process of claim
8.
32. A process for the preparation of polyurethane rigid foams having a
thermal conductivity of 0.02 to 0.024 W/M.multidot..degree.K. consisting
essentially of reacting:
a) organic and/or modified organic polyisocyanates with:
b) lower molecular weight compound having at least two reactive hydrogen
atoms, and optionally;
c) lower molecular weight, chain extending agents, and/or crosslinking
agents;
in the presence of:
d) blowing agents;
e) catalysts and optionally
f) fillers, flame retardants, dyes, pigments, hydrolysis preventing agents,
cell regulators, and/or foam stabilizers selected from the group
consisting of organopolysiloxanes, siloxaneoxyalkylene mixed polymers,
oxyethylated alkylphenols, oxyethylated fatty alcohols, paraffin oils,
castor oil, ricinoleic acid esters, Turkey red oil, and peanut oil;
wherein;
d1) cyclopentane; or,
d2) mixtures comprising:
d2i) cyclopentane, cyclohexane, or a mixture of these cycloalkanes; and
d2ii) compounds having a boiling point less than 35.degree. C.,
homogeneously miscible with cyclopentane and/or cyclohexane
are used as said blowing agent (d).
Description
BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention deals with a process for the preparation of
polyurethane (henceforth abbreviated PU) rigid foams from conventional
starting components in the presence of cyclopentane or mixtures of
cyclopentane and/or cyclohexane and at least one compound homogeneously
miscible with cyclopentane and/or cyclohexane having a boiling point below
35.degree. C. selected from the group consisting of alkanes, cycloalkanes
having a maximum of 4 carbon atoms, dialkylethers, cycloalkylene ethers
and fluoroalkanes, as well as additionally water as a blowing agent. The
present invention also deals with using the PU rigid foams for foaming the
hollow areas in low temperature housing compartments or in heating
elements as well as using these PU rigid foams as insulating material for
composite elements.
2. Description of the Related Art
The preparation of composite or sandwich elements made from a PU rigid foam
and at least one top layer of a rigid or elastic material such as, for
example, paper, plastic films, metal sheets, glass non-wovens, backing
panels, etc. is well known. Also known is foaming the hollow spaces in
household appliances such as, for example, low temperature housing
compartments, that is, refrigerators or freezer chests or hot water tanks
using PU rigid foam as a heat insulating material. In order to avoid
cavities the foamable PU reaction mixture must be injected into the hollow
space which is to be insulated within a short time. To foam such household
appliances, typically low pressure machines, but preferably high pressure
machines are used.
Typical insulating PU rigid foams can be prepared conventionally by
reacting organic polyisocyanates with one or more higher molecular weight
compounds having at least two reactive hydrogen atoms, preferably
polyester polyols and/or polyether polyols as well as typically while
using lower molecular weight chain extending agents and/or crosslinking
agents in the presence of blowing agents, catalysts and optionally
auxiliaries and/or additives. By properly selecting the starting
components one can obtain PU rigid foam having a very low coefficient of
thermal conductivity and good mechanical properties.
A comprehensive overview concerning the preparation of PU rigid foams and
their use as covering layers or preferably core layers in the composite
elements as well as their use as insulation layers in low temperature or
heating technology has been published for example in Polyurethanes,
Plastics Handbook, Vol. 7, 1st Ed. 1966, edited by Dr. R. Vieweg and Dr.
A. Hoechtlen and in the 2nd Edition of 1983 edited by Dr. Gunther Voertel,
Carl-Hanser Verlag, Munich and Vienna.
Chlorofluoroalkanes, preferably trichlorofluoromethane, are used worldwide
on a large scale as blowing agents in the preparation of insulating PU
rigid foams. A disadvantage of these propellant gases is an environmental
burden since they are suspected of contributing to the degradation of the
ozone layer in the stratosphere.
Along with the aforesaid trichlorofluoromethane, other physically effective
blowing agents are also used in the preparation of PU rigid foams. One
example is found in DC-C-1 045 644 (U.S. Pat. No. 3,391,093) which
discloses gaseous hydrocarbons having not more than 3 carbon atoms such as
methane, ethane, ethylene, propane and propylene and halogenated
hydrocarbons such as, for example, chloromethane, dichlorodifluoromethane,
dichlorofluoromethane, chlorodifluoromethane, chloroethane and
dichlorotetrafluoroethane as well as, octafluorocyclobutane, and
hexafluorocyclobutane and hexafluoropropane. Another example is found in
Belgium patent 596,608 which discloses halogen alkanes, such as for
example, 1,1-difluoro-2,2-dichloroethane, 1,2-difluoro-1,2-dichloroethane,
1,1-dichloroethane, 1-fluoro-1,2-dichloroethane,
1-fluoro-2,2-dichloroethane, 1,2-dichloroethane, trichloroethane,
tetrachloroethane, 1-fluoro-1,2,2-trichloroethane, 1-bromoethane, and
1,1,2-trifluoro-2-chloroethane. Another example is found in PCT
Application WO 89/00594 which discloses 1,1,1-trichloroethane which is
used when mixed with other blowing agents.
The aforesaid blowing agents have somewhat of a disadvantage in that they
are toxic, or compared to trichlorofluoromethane they possess a lower gas
yield when blowing PU foam because of their boiling point, or they make
the PU rigid foam have a lower insulating effect, and/or they cause the
foam to shrink. Additionally they lead to the formation of voids in the
foams core or to the partial collapse of the foam even during the foaming
process itself.
Especially the saturated and unsaturated hydrocarbons, specifically
n-pentane, suitable for foaming polystyrene, possess thermal
conductivities which are too high to generate PU rigid foams having the
required insulating properties. Thus, for example, the thermal
conductivity of n-pentane is 150.multidot.10.sup.-4
W/m.multidot..degree.K. and that of n-butane at 25.degree. C. is even
163.multidot.10.sup.-4 W/m.multidot..degree.K.
Another blowing agent is carbon dioxide which according to GD-A 21 16 574
can be dissolved under pressure in at least one starting component for the
preparation of PU rigid foam; said carbon dioxide can be thermally cleaved
from salts such as, for example, carbamates; carbonates such as, for
example, ammonium carbonate, or from bicarbonates, or can be formed from
the reaction of isocyanate with water to form urea groups. Along with the
established industrial processing difficulties when using solid carbon
dioxide or gaseous carbon dioxide under pressure, this method of preparing
PU rigid foams has a significant disadvantage in that the carbon dioxide,
due its very high diffusion rate, diffuses very quickly through the matrix
of the PU foam. In addition, at 25.degree. C. carbon dioxide has a thermal
conductivity of 164.multidot.10.sup.-4 W/m.multidot..degree.K.; this value
lies at the level of that of n-butane and is 85% poorer than the formally
used trichlorofluoromethane.
OBJECTS OF THE INVENTION
The object of the present invention was to prepare polyurethane rigid foams
having a low thermal conductivity, whereby the aforesaid disadvantages
especially with respect to environmental damage and toxicity of the
blowing agent, for example, in the preparation of PU rigid foam would
hopefully be completely eliminated or at least substantially overcome. The
PU rigid foams should be suitable especially for foaming hollow spaces in
low temperature compartment housings and in hot water storage vessels as
well as suitable for an intermediate layer in composite elements.
This object was surprisingly met by using cyclopentane or mixtures of
cyclopentane or cyclohexane and other low boiling point compounds
homogeneously miscible with the aforesaid cycloalkanes as blowing agents,
optionally in conjunction with water.
Description of the Preferred Embodiments
Accordingly, the subject invention pertains to a process for the
preparation of polyurethane rigid foams having a low thermal conductivity,
comprising reacting:
a) organic and/or modified organic polyisocyanates with,
b) at least one higher molecular weight compound having at least two
reactive hydrogen atoms, and optionally
c) lower molecular weight chain extending agents and/or crosslinking
agents, in the presence of
d) blowing agents,
e) catalysts, and optionally
f) auxiliaries and/or additives,
wherein
d1) cyclopentane, or
d2) mixtures containing or preferably comprising,
d2i) cyclopentane, cyclohexane or a mixture of these cycloalkanes, and
d2ii)at least one low boiling point compound homogeneously miscible with
cyclopentane and/or cyclohexane preferably having a boiling point below
35.degree. C.,
are used as said blowing agent d).
The subject invention further pertains to special embodiments of the
subject process and to using the PU rigid foams prepared according to the
present invention as an intermediate layer for composite elements and for
foaming the hollow cavities, preferably in low temperature compartment
housings or in heating elements.
PU rigid foams having a very low thermal conductivity are obtained by using
cyclopentane or mixtures of cyclopentane, cyclohexane or a mixture of
these cycloalkanes and other low boiling point blowing agents which are
used in small quantities to reduce the boiling point of the blowing agent
mixture. Another advantage is that the cycloalkanes used according to the
present invention have a low coefficient of thermal conductivity of about
105.multidot.10.sup.-4 W/m.multidot..degree.K. compared to organic
compounds having a comparable molecular weight. Moreover, their solubility
in the PU matrix is very small so that the permeation rates are extremely
small from the PU rigid foams prepared. Also worth pointing out is the
good compatibility of the PU rigid foam with plastic materials, especially
toughened polystyrene, which are typically used as covering materials in
low temperature appliances. Since these plastics are very resistant
against cycloalkanes, stress cracking corrosion on the plastic covering
layer can be practically eliminated.
Since the PU rigid foams prepared according to the present invention are
further processed preferably having a covering layer, or the formulations
serve to form hollow compartments, the disadvantage caused by the
flammability of the cycloalkanes is predominantly eliminated and
accordingly is negligible.
As already indicated, conventional starting components, except for the
blowing agent are used in the preparation of the PU rigid foams according
to the present invention and the following should be noted with respect to
the conventional starting components.
a) The organic polyisocyanates include all essentially known aliphatic,
cycloaliphatic, araliphatic and preferably aromatic multivalent
isocyanates.
Specific examples include: alkylene diisocyanates with 4 to 12 carbons in
the alkylene radical such as 1,12-dodecane diisocyanate,
2-ethyl-1,4-tetramethylene diisocyanate, 2-methyl-1,5-pentamethylene
diisocyanate, 1,4-tetramethylene diisocyanate and preferably
1,6-hexamethylene diisocyanate; cycloaliphatic diisocyanates such as 1,3-
and 1,4-cyclohexane diisocyanate as well as any mixtures of these isomers,
1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone
diisocyanate), 2,4- and 2,6-hexahydrotoluene diisocyanate as well as the
corresponding isomeric mixtures, 4,4'-, 2,2'-, and
2,4'-dicyclohexylmethane diisocyanate as well as the corresponding
isomeric mixtures and preferably aromatic diisocyanates and
polyisocyanates such as 2,4- and 2,6-toluene diisocyanate and the
corresponding isomeric mixtures, 4,4'-, 2,4'-, and 2,2'-diphenylmethane
diisocyanate and the corresponding isomeric mixtures, mixtures of 4,4'-
and 2,4'-diphenylmethane diisocyanates and polyphenylenepolymethylene
polyisocyanates, mixtures of 4,4'-, 2,4'-, and 2,2'- diphenylmethane
diisocyanates and polyphenylenepolymethylene polyisocyanates, (polymeric
MDI), as well as mixtures of polymeric MDI and toluene diisocyanates. The
organic di- and polyisocyanates can be used individually or in the form of
mixtures.
Frequently, so-called modified multivalent isocyanates, i.e., products
obtained by the partial chemical reaction of organic diisocyanates and/or
polyisocyanates, are used. Examples include diisocyanates and/or
polyisocyanates containing ester groups, urea groups, biuret groups,
allophanate groups, carbodiimide groups, isocyanurate groups and/or
urethane groups. Specific examples include organic, preferably aromatic,
polyisocyanates containing urethane groups and having a NCO content of
33.6 to 15 weight percent, preferably 31 to 21 weight percent, based on
the total weight, e.g., with low molecular weight diols, triols,
dialkylene glycols, trialkylene glycols or polyoxyalkylene glycols with a
molecular weight of up to 1500; modified 4,4'-diphenylmethane diisocyanate
or 2,4- and 2,6-toluene diisocyanate, where examples of di- and
polyoxyalkylene glycols that may be used individually or as mixtures
include diethylene glycol, dipropylene glycol, polyoxyethylene glycol,
polyoxypropylene glycol and polyoxypropylene polyoxyethylene glycols or
-triols. Prepolymers containing NCO groups with a NCO content of 25 to 9
weight percent, preferably 21 to 14 weight percent, based on the total
weight and produced from the polyester polyols and/or preferably polyether
polyols described below; 4,4'-diphenylmethane diisocyanate, mixtures of
2,4'- and 4,4'-diphenylmethane diisocyanate, 2,4- and/or 2,6-toluene
diisocyanates or polymeric MDI are also suitable. Furthermore, liquid
polyisocyanates containing carbodiimide groups and/or isocyanurate rings
and having a NCO content of 33.6 to 15 weight percent, preferably 31 to 21
weight percent, based on the total weight, have also proved suitable,
e.g., based on 4,4'- and 2,4'- and/or 2,2'-diphenylmethane diisocyanate
and/or 2,4- and/or 2,6-toluene diisocyanate.
The modified polyisocyanates may optionally be mixed together or mixed with
unmodified organic polyisocyanates such as 2,4'- and 4,4'-diphenylmethane
diisocyanate, polymeric MDI, 2,4- and/or 2,6-toluene diisocyanate.
The following have proven especially successful as organic polyisocyanates
and are preferred for use in the preparation of polyurethane rigid foams:
mixtures of toluene diisocyanates, and polymeric MDI, or mixtures of
modified urethane groups containing organic polyisocyanates having a NCO
content of from 33.6 to 15 weight percent most preferably, based on
toluene diisocyanates, 4,4'-diphenylmethane diisocyanate, diphenylmethane
diisocyanate isomeric mixtures or polymeric MDI and most preferably,
polymeric MDI having a diphenylmethane diisocyanate isomeric content of
from 30 to 80 weight percent, more preferably from 30 to 55 weight
percent.
b) Preferably, polyhydroxyl compounds having a functionality of 2 to 8,
more preferably 3 to 8, and a hydroxyl number of 150 to 850, more
preferably 350 to 800 are examples of higher molecular weight compounds
(b) having at least 2 reactive hydrogen atoms.
For example, polythioether polyols, polyester amides, polyacetals
containing hydroxyl groups, aliphatic polycarbonates containing hydroxyl
groups, and preferably, polyester polyols and polyether polyols. In
addition, mixtures of at least two of the aforesaid polyhydroxyl compounds
can be used as long as these have an average hydroxyl number in the
aforesaid range.
Suitable polyester polyols can be produced, for example, from organic
dicarboxylic acids with 2 to 12 carbons, preferably aliphatic dicarboxylic
acids with 4 to 6 carbons, and multivalent alcohols, preferably diols,
with 2 to 12 carbons, preferably 2 to 6 carbons. Examples of dicarboxylic
acids include succinic acid, glutaric acid, adipic acid, suberic acid,
azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric
acid, phthalic acid, isophthalic acid and terephthalic acid. The
dicarboxylic acids can be used individually or in mixtures. Instead of the
free dicarboxylic acids, the corresponding dicarboxylic acid derivatives
may also be used such as dicarboxylic acid mono- or di- esters of alcohols
with 1 to 4 carbons, or dicarboxylic acid anhydrides. Dicarboxylic acid
mixtures of succinic acid, glutaric acid and adipic acid in quantity
ratios of 20-35:35-50:20-32 parts by weight are preferred, especially
adipic acid. Examples of divalent and multivalent alcohols, especially
diols, include ethanediol, diethylene glycol, 1,2- and 1,3-propanediol,
dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,
1,10-decanediol, glycerine and trimethylolpropane. Ethanediol, diethylene
glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, or mixtures of at
least two of these diols are preferred, especially mixtures of
1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol. Furthermore, polyester
polyols of lactones, e.g., .epsilon.-caprolactone or hydroxycarboxylic
acids, e.g., .omega.-hydroxycaproic acid, may also be used.
The polyester polyols can be produced by polycondensation of organic
polycarboxylic acids, e.g., aromatic or preferably aliphatic
polycarboxylic acids and/or derivatives thereof and multivalent alcohols
in the absence of catalysts or preferably in the presence of
esterification catalysts, preferably in an atmosphere of inert gases,
e.g., nitrogen, carbon dioxide, helium, argon, etc., in the melt at
temperatures of 150.degree. to 250.degree. C., preferably 180.degree. to
220.degree. C., optionally under reduced pressure, up to the desired acid
value, which is preferably less than 10, especially less than 2. In a
preferred embodiment, the esterification mixture is subjected to
polycondensation at the temperatures mentioned above up to an acid value
of 80 to 30, preferably 40 to 30, under normal pressure and then under a
pressure of less than 500 mbar, preferably 50 to 150 mbar. Examples of
suitable esterification catalysts include iron, cadmium, cobalt, lead,
zinc, antimony, magnesium, titanium and tin catalysts in the form of
metals, metal oxides or metal salts. However, the polycondensation may
also be performed in liquid phase in the presence of diluents and/or
entraining agents such as benzene, toluene, xylene or chlorobenzene for
azeotropic distillation of the water of condensation.
To produce the polyester polyols, the organic polycarboxylic acids and/or
derivatives thereof and multivalent alcohols are preferably polycondensed
in a mole ratio of 1:1-1.8, preferably 1:1.05-1.2.
The resulting polyester polyols preferably have a functionality of 2 to 3,
and a hydroxyl number of 150 to 400, and especially 200 to 300.
However, polyether polyols, which can be obtained by known methods, are
especially preferred for use as the polyhydroxyl compounds. For example,
polyether polyols can be produced by anionic polymerization with alkali
hydroxides such as sodium hydroxide or potassium hydroxide or alkali
alcoholates, such as sodium methylate, sodium ethylate or potassium
ethylate or potassium isopropylate as catalysts and with the addition of
at least one initiator molecule containing 2 to 8, preferably 3 to 8,
reactive hydrogens or by cationic polymerization with Lewis acids such as
antimony pentachloride, boron trifluoride etherate, etc., or bleaching
earth as catalysts from one or more alkylene oxides with 2 to 4 carbons in
the alkylene radical.
Suitable cyclic ethers and alkylene oxides include, for example,
tetrahydrofuran, 1,3-propylene oxide, 1,2- and 2,3-butylene oxide, styrene
oxide and preferably ethylene oxide and 1,2-propylene oxide. The alkylene
cyclic ethers and oxides may be used individually, in alternation, one
after the other or as a mixture. Examples of suitable initiator molecules
include water, organic dicarboxylic acids such as succinic acid, adipic
acid, phthalic acid and terephthalic acid, aliphatic and aromatic,
optionally N-mono-, N,N-, and N,N'-dialkyl substituted diamines with 1 to
4 carbons in the alkyl radical, such as optionally mono- and
dialkyl-substituted ethylenediamine, diethylenetriamine,
triethylenetetramine, 1,3-propylenediamine, 1,3- and 1,4-butylenediamine,
1,2-, 1,3-, 1,4-, 1,5- and 1,6-hexamethylenediamine, phenylenediamines,
2,3-, 2,4- and 2,6-toluenediamine and 4,4'-, 2,4'- and
2,2'-diaminodiphenylmethane.
Suitable initiator molecules also include alkanolamines such as
ethanolamine, diethanolamine, N-methyl- and N-ethylethanolamine, N-methyl-
and N-ethyldiethanolamine and triethanolamine plus ammonia.
Multivalent alcohols, especially divalent and/or trivalent alcohols are
preferred such as ethanediol, 1,2-propanediol and 1,3-propanediol,
diethylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol,
glycerine, trimethylolpropane, pentaerythritol, sorbitol and sucrose.
The polyether polyols have a functionality of preferably 3 to 8 and
especially 3 to 6 and have a hydroxyl number of 300 to 850, preferably 350
to 800.
Also suitable as polyether polyols are: melamine polyether polyol
dispersions according to EP A 23 987 (U.S. Pat. No. 4,293,657); polymer
polyether polyol dispersions prepared from polyepoxides and epoxide resin
hardeners in the presence of polyether polyols according to DE 29 43 689
(U.S. Pat. No. 4,305,861); dispersions of aromatic polyesters in
polyhydroxyl compounds according to EP A 62 204 (U.S. Pat. No. 4,435,537)
or according to DE A 33 00 474; dispersions of organic and/or inorganic
fillers in polyhydroxyl compounds according to EP A 11 751 (U.S. Pat. No.
4,243,755); polyurea polyether polyol dispersions according to DE A 31 25
402; tris-(hydroxyalkyl)-isocyanurate polyether polyol dispersions
according to EP A 136 571 (U.S. Pat. No. 4,514,526) and crystallite
suspensions according to DE A 33 42 176 and DE A 33 42 177 (U.S. Pat. No.
4,560,708), whereby the details in the aforesaid patents are to be
regarded as a part of the patent disclosure, and are herein incorporated
by reference.
Like the polyester polyols, the polyether polyols may be used either
individually or in the form of mixtures. Furthermore, they can be mixed
with the aforesaid dispersions, suspensions, or polyester polyols as well
as the polyester amides containing hydroxyl groups, the polyacetals,
and/or polycarbonates.
Examples of hydroxyl group-containing polyacetals that can be used include,
for example, the compounds that can be produced from glycols such as
diethylene glycol, triethylene glycol,
4,4'-dihydroxyethoxydiphenyldimethylmethane, hexanediol and formaldehyde.
Suitable polyacetals can also be produced by polymerization of cyclic
acetals.
Suitable hydroxyl group-containing polycarbonates include those of the
known type such as those obtained by reaction of diols, e.g.,
1,3-propanediol, 1,4-butanediol and/or 1,6-hexanediol, diethylene glycol,
triethylene glycol or tetraethylene glycol and diaryl carbonates, e.g.,
diphenyl carbonate, or phosgene.
The polyester amides include the mainly linear condensates obtained from
multivalent saturated and/or unsaturated carboxylic acids and their
anhydrides and amino alcohols, or mixtures of multivalent alcohols and
amino alcohols and/or polyamines.
Mixtures which have proven most preferred as polyhydroxyl compounds and
which are thus preferably used are those which, based on 100 parts by
weight, comprise:
bi) up to 95 parts by weight, more preferably 20 to 80 parts by weight of a
polyether polyol initiated with sucrose having a hydroxyl number of from
300 to 500, more preferably 350 to 450, based on 1,2-propylene oxide or
1,2-propylene oxide and ethylene oxide;
bii) up to 15 parts by weight, more preferably 5 to 15 parts by weight of a
polyether polyol initiated with sorbitol having a hydroxyl number of from
400 to 600, more preferably 450 to 550, based on 1,2-propylene oxide or
1,2-propylene oxide and ethylene oxide;
biii) up to 20 parts by weight, more preferably 5 to 15 parts by weight of
a polyether polyol initiated with ethylenediamine having a hydroxyl number
of from 700 to 850, more preferably 750 to 800, based on 1,2-propylene
oxide; and
biv) up to 60 parts by weight, more preferably 5 to 40 parts by weight of a
polyether polyol having a hydroxyl number of from 400 to 600, more
preferably 450 to 550, based on 1,2-propylene oxide or 1,2-propylene oxide
and ethylene oxide prepared while using a mixture of sucrose and
triethanolamine in a weight ratio of from 1:2 to 2:1 as an initiator
molecule.
c) The polyurethane rigid foams can be prepared with or without using chain
extending agents and/or crosslinking agents. To modify the mechanical
properties, however, it has proven advantageous to add chain extenders,
crosslinking agents or optionally mixtures thereof. Suitable chain
extenders and/or crosslinking agents include preferably alkanolamines,
more preferably diols and/or triols with molecular weights of less than
400, preferably 60 to 300. Typical examples are alkanolamines such as, for
example, ethanolamine and/or isopropanolamine; dialkanolamines, such as,
for example, diethanolamine, N-methyl-, N-ethyldiethanolamine,
diisopropanolamine; trialkanolamines such as, for example,
triethanolamine, triisopropanolamine; and the addition products from
ethylene oxide or 1,2-propylene oxide, and alkylenediamines having 2 to 6
carbon atoms in the alkylene radical such as, for example,
N,N'-tetra(2-hydroxyethyl)-ethylenediamine and
N,N'-tetra(2-hydroxypropyl)ethylenediamine, aliphatic, cycloaliphatic
and/or araliphatic diols having 2 to 14, more preferably 4 to 10 carbon
atoms such as, for example, ethylene glycol, 1,3-propanediol,
1,10-decanediol, o-, m-, p-dihydroxycyclohexane, diethylene glycol,
dipropylene glycol, and preferably 1,4-butanediol, 1,6-hexanediol, and
bis-(2-hydroxyethyl)-hydroquinone; triols such as 1,2,4-, and
1,3,5-trihydroxycyclohexane, glycerine and trimethylolpropane; and lower
molecular weight hydroxyl group containing polyalkylene oxides, based on
ethylene oxide and/or 1,2-propylene oxide and aromatic diamines such as,
for example, toluene diamines and/or diaminodiphenylmethanes as well as
the aforesaid alkanolamines, diols, and/or triols as initiator molecules.
If chain extending agents, crosslinking agents, or mixtures thereof are
used in the preparation of polyurethane rigid foams, then advantageously
these are used in a quantity of from up to 20 weight percent, more
preferably 2 to 5 weight percent, based on the weight of the polyhydroxyl
compound.
d) Preferably cyclopentane (d1) is used as a blowing agent in the
preparation of the PU rigid foam. However, mixtures (d2) comprising:
d2i) cyclopentane, cyclohexane or a mixture of the aforesaid cycloalkanes,
and
d2ii) at least one low boiling point compound homogeneously miscible with
cyclopentane and/or cyclohexane, preferably a compound having a boiling
point below 35.degree. C.
have proven very effective as well.
Suitable compounds of the aforesaid type used as blowing agents can be
selected from the group consisting of alkanes, cycloalkanes having a
maximum of 4 carbon atoms, dialkylethers, cycloalkylene ethers and
fluoroalkanes. Mixtures of at least two compounds from the aforesaid group
can also be used. Individual examples are: alkanes, such as, for example,
propane and butane or isobutane; cycloalkanes such as, for example,
cyclobutane; dialkylethers, such as, for example, dimethylether,
methylethylether or diethylether; cycloalkylene ethers such as, for
example, furan and fluoroalkanes which break down in the troposphere and
thus do not damage the ozone layer, such as, for example,
trifluoromethane, difluoromethane, difluoroethane, tetrafluoroethane and
heptafluoropropane.
The blowing agents used according to the present invention can be used
alone or preferably in conjunction with water, whereby the following
combinations are preferred and thus they are efficatiously used: water and
cyclopentane; water, cyclopentane, cyclohexane or a mixture of these
cycloalkanes and at least one compound selected from the group consisting
of n-butane, isobutane, cyclobutane, dimethylether, diethylether, furan,
trifluoromethane, difluoromethane, difluoroethane, tetrafluoroethane and
heptafluoropropane. The quantity of low boiling point compounds
homogeneously miscible with cyclopentane and/or cyclohexane used in
combination with cyclopentane and most preferably with cyclohexane, is
measured so that the resulting mixture has a boiling point below
50.degree. C., more preferably 30.degree. C. to 0.degree. C. The required
quantity for this depends on the plot of the boiling point curve of the
mixture and can be experimentally determined according to known methods.
PU rigid foams having a low conductivity are especially obtained if the
following is used as the blowing agent (d) per 100 parts by weight of
starting component (b):
d1) 3 to 22 parts by weight, more preferably 5 to 18 parts by weight and
most preferably 8 to 14 parts by weight of cyclopentane and 0 to 7 parts
by weight, more preferably 2.0 to 5.0 parts by weight and most preferably
2.2 to 4.5 parts by weight of water or,
d2i) 2 to 22 parts by weight, more preferably 5 to 19 parts by weight and
most preferably 9 to 19 parts by weight cyclopentane and/or cyclohexane,
and
d2ii) 0.1 to 18 parts by weight, more preferably 0.5 to 10 parts by weight
and most preferably 1.0 to 6.0 parts by weight of at least one compound
having a boiling point below 35.degree. C. homogeneous miscible with
cyclopentane and/or cyclohexane, said compound is selected from the group
consisting of alkanes, cycloalkanes having a maximum of 4 carbon atoms,
dialkyl ethers, cycloalkylene ethers and preferably fluoroalkanes and 0 to
7 parts by weight, more preferably 2.0 to 5.0 parts by weight and most
preferably 2.2 to 4.5 parts by weight of water.
When preparing the preparing the PU rigid foam the cyclopentane (d1) or the
blowing agent mixture (d2) optionally combined with water is incorporated
following conventional methods into at least one of starting components
(a) through (c) for preparing the PU rigid foam optionally under pressure,
or it is directly added to the reaction mixture typically by means of a
suitable mixing device.
e) Suitable catalysts (e) include especially compounds that greatly
accelerate the reaction of the hydroxyl group containing compounds of
components (b) and optionally (c) with the polyisocyanates. Examples
include organic metal compounds, preferably organic tin compounds such as
tin(II) salts of organic carboxylic acids, e.g., tin(II) acetate, tin(II)
dioctoate, tin(II) ethylhexoate and tin(II) laurate, as well as the
dialkyltin(IV) salts of organic carboxylic acids, e.g., dibutyltin
diacetate, dibutyltin dilaurate, dibutyltin maleate, and dioctyltin
diacetate. The organic metal compounds are used alone or preferably in
combination with strong basic amines. Examples include amines such as
2,3-dimethyl-3,4,5,6-tetrahydropyrimidine, tertiary amines such as
triethylamine, tributylamine, dimethylbenzylamine, N-methylmorpholine,
N-ethylmorpholine, N-cyclohexylmorpholine,
N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethyl-butanediamine,
or -hexanediamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl
ether, bis(dimethylaminopropyl) urea, dimethylpiperazine,
1,2-dimethylimidazole, 1-aza-bicyclo[3.3.0]octane and preferably
1,4-diaza-bicyclo[2.2.2]octane and alkanolamine compounds such as
triethanolamine, triisopropanolamine, N-methyl- and N-ethyldiethanolamine
and dimethylethanolamine.
Suitable catalysts include tris-(dialkylamino)-s-hexahydrotriazines,
especially tris(N,N-dimethylaminopropyl)-s-hexahydrotriazine,
tetraalkylammonium hydroxides such as tetramethylammonium hydroxide,
alkali hydroxides such as sodium hydroxide and alkali alcoholates such as
sodium methylate and potassium isopropylate as well as alkali salts of
long-chain fatty acids with 10 to 20 carbons and optionally OH pendent
groups. 0.001 to 5 weight percent, especially 0.05 to 2 weight percent, of
catalyst or catalyst combination, based on the weight of component (b) is
preferred.
f) Optionally other additives and/or auxiliaries (f) may be incorporated
into the reaction mixture to produce the polyurethane rigid foam. Examples
include surface active substances, foam stabilizers, cell regulators,
fillers, dyes, pigments, flame retardants, hydrolysis preventing agents,
fungistatic and bacteriostatic agents.
Examples of surface active substances include compounds that support the
homogenization of the starting materials and are optionally also suitable
for regulating cell structure. Examples include emulsifiers such as the
sodium salts of castor oil sulfates or of fatty acids as well as salts of
fatty acids with amines, e.g., diethanolamine oleate, diethanolamine
stearate, diethanolamine ricinoleate, salts of sulfonic acids, e.g.,
alkali or ammonium salts of dodecylbenzenesulfonic acid or
dinaphthylmethanedisulfonic acid and ricinoleic acid; foam stabilizers
such as siloxaneoxalkylene mixed copolymers and other organopolysiloxanes,
oxethylated alkylphenols, oxethylated fatty alcohols, paraffin oils,
castor oil and ricinoleic acid esters, Turkey red oil and peanut oil; as
well as cell regulators such as paraffins, fatty alcohols and dimethyl
polysiloxanes. Furthermore, the oligomeric acrylates with polyoxyalkylene
and fluoroalkane side groups are also suitable for improving the
emulsifying effect, the cell structure and/or for stabilizing the foam.
These surface-active substances are generally used in amounts of 0.01 to 5
parts by weight based on 100 parts by weight of component (b).
Fillers, especially reinforcing fillers, are understood to refer to the
known conventional organic and inorganic fillers, reinforcing agents,
weighting agents, agents to improve abrasion properties in paints,
coatings agents, etc. Specific examples include inorganic fillers, such as
silicate minerals, such as layered silicates; e.g. antigorite, serpentine,
hornblends, amphiboles, chrysotile, talc; metal oxides such as kaolin,
aluminum oxides, aluminum silicate, titanium oxides and iron oxides, metal
salts such as chalk, heavy spar; and inorganic pigments such as cadmium
sulfide, zinc sulfide as well as glass particles. Examples of organic
fillers include carbon black, melamine, colophony, cyclopentadienyl resins
and graft polymers.
The organic and inorganic fillers may be used individually or as mixtures
and are advantageously incorporated into the reaction mixture in amounts
of 0.5 to 50 weight percent, preferably 1 to 40 weight percent, based on
the weight of components (a) to (c).
Suitable flame retardants include, for example, tricresyl phosphate,
tris-(2-chloroethyl)-phosphate, tris-(2-chloropropyl)phosphate,
tris-(2,3-dibromopropyl)phosphate, tris(1,3-dichloropropyl)phosphate and
tetrakis-(2-chloroethyl)-ethylene diphosphate.
In addition to the aforementioned halogen substituted phosphates, inorganic
flame retardants may also be used such as red phosphorus, aluminum
hydroxide, antimony trioxide, arsenic oxide, aluminum polyphosphate and
calcium sulfate; or cyanuric acid derivatives such as melamine or mixtures
of at least two flame retardants, such as for example, ammonium
polyphosphates and melamine, plus optionally starches for making the PU
rigid foam of the present invention flame resistant. In general, it has
proven advantageous to use 5 to 50 parts by weight, preferably 5 to 25
parts by weight, of the aforementioned flame retardants or mixtures
thereof for each 100 parts by weight of components (a) through (c).
Details regarding the aforementioned other conventional additives and
auxiliaries can be obtained from the technical literature, e.g., the
monograph by J. H. Sauders and K. C. Frisch "High Polymers," volume XVI,
Polyurethanes, parts 1 and 2, Interscience Publishers, 1962 and 1964, or
in the Plastics Handbook, Polyurethanes, volume VII, Carl Hanser
Publishers, Munich, Vienna, lst and 2nd editions, 1966 and 1983.
To prepare the polyurethane rigid foam, the organic, optionally modified
polyisocyanates (a), the higher molecular compounds (b) having at least 2
reactive hydrogen atoms, and optionally the chain extending agents and/or
crosslinking agents (c) are reacted in such quantities so that the
equivalent ratio of NCO groups from the polyisocyanates (a) to the total
of the reactive hydrogen atoms of the (b) components and optionally (c) is
from 0.85 to 1.25:1 more preferably 0.95 to 1.15:1 and, most preferably
approximately 1.0 to 1.10:1. If the urethane group containing foams are
modified by the formation of isocyanurate groups, for example, to increase
flame resistance, then typically one employs a ratio of the NCO groups
from polyisocyanates (a) to the total of the reactive hydrogen atoms of
components (b) and optionally (c) of 1.5 to 10:1, more preferably 1.5 to
6:1.
The PU rigid foams can be prepared batchwise or continuously according to
the prepolymer process or more preferably according to the one-shot
process with the help of conventional mixing equipment.
It is proven especially advantageous to work according to the 2-component
process and to incorporate starting components (b), (d), (e) and
optionally (c) and (f) into the (A) component and to use the organic
polyisocyanates, modified polyisocyanates (a) or mixtures of the aforesaid
polyisocyanates and optionally blowing agent (d) as the (B) component.
The starting components are mixed at a temperature of 15 to 90.degree. C.,
more preferably 20 to 35.degree. C. and introduced into an open,
optionally heated mold where the reaction mixture is allowed to foam
essentially pressure free to avoid a compressed peripheral zone. To form
composite elements, typically the backside of a top layer is coated, for
example, by applying a coating or spraying, with a foamable reaction
mixture then this is allowed to foam and cure into PU rigid foam.
The PU rigid foams prepared according to the present invention preferably
have densities from 20 to 50 g/1 and possess a thermal conductivity of
0.020 to 0.024 W/m.multidot..degree.K.
The PU rigid foams are preferably used as insulating intermediate layers in
composite elements and to foam hollow spaces in low temperature
compartment housings, especially for refrigerators and deep chest freezers
and said foams are used as exterior shells for hot water storage tanks.
Products are also suitable to insulate heated materials or as motor
coverings and as pipe shells.
EXAMPLE 1
Preparation of the Polyurethane Rigid Foam
A Component:
A mixture comprising:
______________________________________
82.4 parts by weight of a polyether polyol having a
hydroxyl number of 400 prepared by the anionic
addition polymerization of 1,2-propylene oxide on
sucrose,
3.6 parts by weight of water,
2.3 parts by weight of N,N-dimethylcyclohexylamine
0.8 parts by weight of a foam stabilizer based on a
silicone (Tegostab .RTM. B 8409 from Goldschmitt AG,
Essen, FRG), and
10.9 parts by weight of cyclopentane.
______________________________________
B Component:
A mixture of diphenylmethane diisocyanates and polyphenyl polymethylene
polyisocyanates (polymeric MDI, NCO content 31 weight percent).
100 parts by weight of the A component and 148 parts by weight of the B
component were intensively mixed at 23.degree. C. using a high speed
stirrer at 2000 rpm, then the reaction mixture was poured into an open
carton whose internal dimensions were 20.times.20.times.20 cm and it was
allowed to foam.
Obtained was a uniform PU rigid foam having an average cell diameter of 300
microns, a thermal conductivity measured at 10.degree. C. of 0.021
W/m.multidot..degree.K. and having a density of 22 g/l.
EXAMPLE 2
A Component:
A mixture comprising:
______________________________________
80.8 parts by weight of a polyether polyol having a
hydroxyl number of 400 prepared by the anionic
addition polymerization of 1,2-propylene oxide on
sucrose,
2.0 parts by weight of water,
2.3 parts by weight of N,N-dimethylcyclohexylamine,
0.8 parts by weight of a foam stabilizer based on a
silicone (Tegostab .RTM. B 8409), and
14.1 parts by weight of a blowing agent mixture having a
boiling point of approximately 25.degree. C. comprising 13.5
parts by weight of cyclohexane and 0.6 parts by
weight of heptafluoropropane.
______________________________________
B Component: Analogous to Example 1
100 parts by weight of the A component and 119 parts by weight of the B
component are reacted analogous to the teachings of example 1.
Obtained was a PU rigid foam having a density of 21 g/1 and a thermal
conductivity measured at 10.degree. C. of 0.023 W/m.multidot..degree.K.
EXAMPLE 3
A Component:
A mixture comprising,
______________________________________
81.4 parts by weight of a polyether polyol having a
hydroxyl number of 400 prepared by the anionic
addition polymerization of 1,2-propylene oxide and
sucrose,
3.5 parts by weight of water,
2.3 parts by weight of N,N-dimethylcyclohexylamine
0.8 parts by weight of a foam stabilizer based on
silicone (Tegostab .RTM. B 8409), and
12.0 parts by weight of a blowing agent mixture compris-
ing 8 parts by weight of cyclopentane and 4 parts
by weight of diethylether.
______________________________________
B Component: analogous to example 1.
100 parts by weight of the A component and 145 parts by weight of the B
component were reacted analogous to the teachings of example 1. Obtained
was PU rigid foam having a density of 23 g/1 and a thermal conductivity
measured at 10.degree. C. of 0.022 W/m.multidot..degree.K.
EXAMPLE 4
A Component:
A mixture comprising:
______________________________________
82.9 parts by weight of a polyether polyol having a
hydroxyl number 400 prepared by the anionic
addition polymerization of 1,2-propylene oxide on
sucrose,
3.0 parts by weight of water,
2.3 parts by weight of N,N-dimethylcyclohexylamine,
0.8 parts by weight of a foam stabilizer based on
silicone (Tegostab .RTM. B8409), and
11.0 parts by weight of a blowing agent mixture compris-
ing 8 parts by weight cyclopentane and 3 parts by
weight isobutane.
______________________________________
B Component: Analogous to example 1.
100 parts by weight of the A component and 138 parts by weight of the B
component were reacted analogous to the teachings of example 1. Obtained
was PU rigid foam having a density of 24 g/1 and a thermal conductivity of
0.024 W/m.multidot..degree.K.
EXAMPLE 5
A Component:
A mixture comprising:
______________________________________
79.1 parts by weight of a polyether polyol having a
hydroxyl number of 400 prepared by the anionic
addition polymerization of 1,2-propylene oxide on
sucrose,
1.8 parts by weight of water,
2.3 parts by weight of N,N-dimethylcyclohexylamine,
0.8 parts by weight of a foam stabilizer based on
silicone (Tegostab .RTM. B 8409), and
16.0 parts by weight of a blowing agent mixture compris-
ing 15 parts by weight of cyclohexane and 1 part by
weight of tetrafluoroethane.
______________________________________
B Component: Analogous to Example 1.
100 parts by weight of the A component and 114 parts by weight of the B
component were reacted analogous to the teachings of example 1. Obtained
was PU rigid foam having a density of 24 g/1 and a thermal conductivity
measured at 10.degree. C. of 0.022 W/m.multidot..degree.K.
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